Ah... I understand the mechanic now, but I don't think that's explained very well in the initial post.
My concern isn't really about balance; it's that it's an immersion-bending and unnecessarily complicated combat tactic that rewards players who micromanage the rules. I've never seen a new player think of anything like that, because it doesn't really make sense. If the casting system is balanced around the assumption that casters can't be disrupted by AoOs while casting, then casters played by people who don't do those shenanigans will be weaker. To solve that, the mechanic should be made into a core part of the system, rather than only being accessible to a small subset of the player base. If the casting system isn't balanced around that assumption, then players who do those shenanigans will gain an unfair advantage.
Ahh - so that mechanic prevents all monsters from suddenly getting an AC bonus. That makes sense.
Distance matters because the line is still drawn from the centers of the flanking characters' squares. When attacking from reach, the center of a character's square may not have any relationship to the square they are effectively attacking from. Here, I drew a table below to illustrate the point:
E2 E3 E0 E1 C E0 E4
You can see that none of E1, E2, E3, and E4 are now flanking - or perhaps they would just barely scrape into flanking, depending on how precise your center-measuring is. In fact, I think several more Es could be added without creating a single flanking position.
I saw that, but with the attack penalties from iterative attacks, you probably will miss on a 1 against any reasonable foe with most of your attacks. I haven't done rigorous combat math for this overhaul. But if the system is designed such that, in a typical combat, you hit on a 1 with most or all of your attacks, I would seriously question whether attack bonus and armor class are balanced correctly. Sure, you're not likely to fumble much against a commoner. But you'll still fumble unreasonably often.
Suppose, without doing any math, that you hit on a 1 with your full BAB attacks, but can miss on a 1 with all other attacks; that seems plausible to me. A 20th level warrior makes 4 attacks per round from BAB alone, disregarding all features and magic effects that would grant extra attacks (well, 5 per round with the move action attack, but since that is full BAB we can ignore it). That means they make three attacks per round with a chance to fumble, for a total of (1 - 0.95*0.95*0.95) = 15% chance to fumble every round. That seems absurd to me, given the demigod-level skill that a 20th level warrior is supposed to have.
Where does it say the tradeoff is 2:1? The pathfinder Combat Expertise is 1:1. In any event, the core problem is that most of the time, your personal AC doesn't really matter in a group fight, because the optimal strategy is to focus all attacks on a single member of the opposing group - that's the only way to take someone out of a fight (ignoring save-or-lose effects, which are irrelevant to AC anyway). If you are the one getting focused down, then yes, you should be using the defensive expertise. But more likely, the enemy is focusing down someone else, so you will suffer no meaningful penalty for dropping your AC through the floor. Essentially, every physical combatant* in a combat should be using either the defensive expertise or the offensive expertise every round - the combat tactics just determine which is which.
Now, maybe that's a system you're fine with - and I'm not actually saying it's imbalanced, per se. It's just vastly more micromanage-y than I would want from a system. It means your core combat numbers change all the time, which slows down play.
* What's the generic term for "person who hits stuff with pointy sticks" in this overhaul? I would normally say "warrior", but that's a class now...
Yeah, if you rest overnight you should be fairly well healed. But short rests heal a totally insignificant amount of HP.
In PF, the "long term care" action specifically takes 8 hours to perform, so you couldn't use it with short rests. Do you intend to change it so long term care can be performed with short rests?
Got it - that makes sense. I think it could be explained slightly more clearly, but the mechanic makes sense.
All of those things mean the optimal magic item strategy is harder to execute on. But that doesn't change the fact that the optimal magic item strategy is very christmas tree-like. Maybe it wouldn't come up enough in a typical campaign to matter, but I would expect those incentives to still cause problems.
Makes sense.
Yes, the giant is disproportionately massive, but I feel like that would just make his footsteps so heavy that his feet push right through the grease to the solid floor. When he walks on ice, he would crack the ice so much it wouldn't be slippery at all for him. I think I understand where you're coming from - a giant should be less able to right himself after being pushed off balance, which is kind of a Balance check. But I don't think the overall mechanical impact of being larger is a net penalty to Balance checks. It's arguable, I'll grant you. I guess my concern is that spells like Grease, and other trivial environmental challenges, suddenly become almost unstoppable when used against sufficiently massive creatures who didn't train Balance (which is a rare skill to have trained, and doesn't scale with level otherwise). That seems... bizarre.
Oh, I haven't the faintest idea how seige combat works, and have never cared enough to develop it properly. But I think one of the 3.5 sourcebooks, like the Miniatures Handbook, had a fairly detailed treatment of seige warfare. Why not leave that as is instead of adding your own mechanics?
I'm happy with that.
Do you think the combat maneuvers are currently useful in an actual combat without the feats? I would say no, or at least not in more than perhaps 5% of combats with extraordinary circumstances. Side note, since it's unclear: is initiating a grapple still a standard action?